What Should Be the Cut Point for Classification Criteria of Studies in Gout? A Conjoint Analysis

To determine the acceptable level of positive predictive value (PPV) and negative predictive value (NPV) for classification criteria for gout, given the type of study.

We conducted an international web-based survey with 91 general practitioners and rheumatologists experienced in gout. Conjoint analysis was used as the framework for designing and analyzing pairs of 2 profiles, each describing a study type, a PPV, and an NPV. There were 5 study types presented: a phase III randomized controlled trial (RCT) of a nonsteroidal antiinflammatory drug versus prednisone for acute gout flares, a phase III RCT of a biologic agent for acute gout flares, a phase II RCT of a novel uricosuric drug of unknown efficacy and limited toxicity data, a case-control, genome-wide association study of gout, and a cohort study examining long-term outcomes of gout. PPV and NPV both had 5 levels ranging from 60-99%.

The panelists in majority were male (65%) rheumatologists (93%) with an average of 19 years of practice, seeing 5 to 60 gout patients monthly. PPV was most highly weighted in decision making: the relative importance was 59% for PPV, 29% for NPV, and 13% for study type. The preferred PPV was 90% or 80%, with an accompanying NPV of 70% or 80%, dependent on study type.

Preferred PPVs and NPVs range between 70% and 90% and differ by study type. A single cut point can be a reasonable approach for all study types if a PPV of 90% and NPV of 80% is approximated.